Process for making integral color correction masks



March 31, 1953 A. B. JENNINGS 2,633,422

pnocass FOR' MAKING INTEGRAL 001.01: CORRECTION MASKS Filed April 21, 1948 (D z .40 I I m TOTALDENSV '7 .20 LOO ,a-TRUE' NIEUTRAL .80 gusrrv v /CYAN .60

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ANDREW BRADSHAW JENNINGS ATTORNEY Patented Mar. 31, 1953 PROCESS FOR MAKING INTEGRAL COLOR CORRECTION MASKS Andrew Bradshaw Jennings, New Brunswick,

N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application April 21, 1948, Serial No. 22,300

4 Claims.

This invention relates to processes of color photography. More particularly it relates to processes of duplicating subtractive color reproductions of an original scene. Still more particularly it relates to such processes wherein color correction of subtractive colors is accomplished by a novel integral masking procedure.

subtractive three-color reproduction processes utilize three colorants which are complementary in color, respectively, to three primary analysis colors. The analysis colors are red, green, and blue, and the colorants, cyan (blue-green), magenta, and yellow. Facsimile reproduction of a colored subject is never achieved because no set of three subtractive colorants, e. g., dyes, pigments, etc., with ideal spectral absorption are known. Cyan colorants, for example, absorb in both the blue and green region of the spectrum. Magenta colorants absorb in the blue and red regions of the spectrum, and yellow colorants ab-; sorb in the green region of the spectrum.

It has been previously proposed to employ colored couplers for masking but it was difficult, if not impossible, to find such compounds capable of yielding correct density and contrast values for both the primary color component image and the, masking images. In order to overcome this difficulty it has been proposed to utilize mixtures of colored and colorless coupler which yield dyes of the same hue on color development. Even this method, however, suffers from the difficulty of finding such combinations in which the colored and uncolored couplers are capable of coupling at the proper rate in relation to each other. Moreover, the use of colored substances in the lightsensitive layers of a photographic element introduces filtering effects, thereby reducing the eliective sensitivity of the element. The use of colored couplers in a photographic element imposes severe limitations on the choice of layer arrangements and precludes the use of such elements for any other purpose.

The present invention avoids all of these disadvantages and provides a method of great flexibility for controlling color reproduction as is shown in subsequent paragraphs.

An object of this invention is to improve the duplication of subtractive color reproductions. Another object is to provide a practical manner of correcting the undesirable absorption of subtractive color formers. A further object is to provide a practical method of correcting the undesirable absorption of subtractive color formers by the generation of colored masks in the layers containing color-developed dye images. Still l 2 other objects will be apparent from the following description of the invention.

It has been found that the deficiencies of cyan and magenta color-developed quinoneimine. or azomethine dye images, whereby they absorb in the blue and green and blue regions, respectively, of the spectrum, can be compensated for by superimposing on the cyan and magenta image components colored masks which absorb in the regions of undesired absorptions, which they are intended to correct, by a dye coupling and preferably an azo coupling procedure in which the residual color formers in the image areas and reverse areas couple whereby a dye. e. g., an azo dye of spectral properties difiering from those of the quinoneimine or azomethine dye images, is formed. The silver and silver salts are removed, leaving the dye images and integral color mask. When the resulting image-bearing layer is printed onto a light-sensitive photographic element,

the undesirable absorption characteristics of the dye images are automatically compensated for.

The invention is especially useful in the treatment of multilayer monopack film elements:

which contain light-sensitive silver halide layers and subtractive cyan, magenta, and yellow color formers in the appropriate layers.

gion of the spectrum. The film element is first exposed in a camera or from separation records, or from a positive subtractive color transparency,

then developed in an aqueous developer solution containing a primary aromatic amino developing agent to yield cyan, magenta, and yellow dye im- The element is then subjected to a dye-generation such that the residual cyan (minus-red) color former ages in situ with metallic silver images.

is converted into an orange dye and the residual magenta (minus-green) color former is converted into a yellow dye in the respective layers. The colored masks which are produced are of a contrast opposite in sign to that of the primary images since the density of masking dye in any area is inversely proportional to the density of the color-developed dye image in that area. The

contrast and density of the mask images may .be

varied, thus making the process one of great ver- The yellow color formers need not be compensated for because of their slight absorption in the green remoans-Q H (l H:

Ha I The quinoneimine dyes which may be obtained from these dye intermediates by interaction with oxidized p-amino diethylaniline may be represented in the form of a composite plot of their spectrophotometric curves as shown in Figure I of the accompanying drawing. In this figure, the densities orv the individual components have been chosen to yield the closest approximation to composite neutral. The total density of the three components at each wave length is represented by the irregular black line in the vicinity of the horizontal axis corresponding to density 1.0. True neutral, as represented by the straight line at density 1.0 will never be achieved with any mixture of three real subtractive printing colors, but it should be recognized that the irregular black line represents a visually acceptable neutral. This selection of neutral density 1.0 has been made because it will be apparent that the densities of the individual color components are proportional to their relative contrasts. The term density in this specification, as referred to a color component, is the maximum density as read from the spectrophotometric curve.

In making a tricolor analysis of the film represented in the figure, three monochromatic bands of wave lengths 440, 540, and 660 millimicrons are used. It will be noted that at each of these wave lengths, density is contributed by all three components. Specifically, these densities may be tabulated as follows:

Table I 440 mu I 540 Inn 660 mu .64 .04 .00 .39 1.02 .06 Cyan l2 l0 96 Consider now the function of the magenta image component: ideally it should modulate only the green analysis primary; yet, it exhibits a small amount of density in the red region which, in fact, can be ignored, but a very appreciable absorption of blue light is evident which cannot be ignored. If, however, a mask derived from the magenta image component be superimposed upon the monopack, cancellation of the efiective absorption of blue light by the magenta component will have been realized provided that the contrast of the mask is opposite in sign and proportional to the ratio of blue to green densities of the magenta component. This mask should have selective absorption for blue. In other words, it may be yellow. Thus it is seen that the blue absorption of the magenta subtractive primary may be compensated for by means of a mask of opposite gamma which absorbs blue light. The numerical value of the gamma of the mask is dependent upon the amount of undesired blue absorption by the magenta component.

The cyan component of the figure exhibits undesirable absorption in both the blue and green portions of the spectrum. A correcting mask which absorbs in both regions, to avoid contamination of blue and green primary analysis records, should be orange-red in color and the com trast of the mask may be determined, as above, in accordance with the relative absorption of green and blue by the cyan component. The yelq' low subtractive primary of the figure is reasonably satisfactory and requires no correction.

Multilayer monopack films which contain the integral masks described above in the magenta and cyan dye image layers can be used in several ways, e. g.,

1. As a color negative camera film for original recording.

2. As a color reversal positive camera film for original recording.

As a dupe color negative serving as an intermediate step in reproducing from a positive (reversal) monopack original or from primary analysis black and white separation records.

The preferred method of forming the color masks in the image-bearing layers as described above is by azo coupling. This may be carried out by means of diazonium salt solutions, stabilized diazo compounds, or by means of the ac-,-

tion of hydrazines and derivatives of hydrazines' together with exposed silver salts. Preferred diazo compounds for use in the production of the required orange and yellow masks from color coupling components of the conventional type are those derived from aromatic amines with electrophyllic substituents such as COOI-I, SOaH. -NO2, halogen, CN, and CFa.

In processes of automatic integral masking which have been proposed heretofore, it is usually necessary to maintain a normal" arrangement of layer sensitivity and respective color generating capacity for those layers. This normal arrangement involves the use of an outermost blue-sensitive layer which is subsequently converted into a yellow image component. The remaining layers are usually green and red-sensitive in that order, each layer being responsible for an image component in its complementary color.

In a preferred form of the present invention, a self-masking color duplicate negative may be used to print multiple copies of color corrected positive prints. For processes of color cinematography which require an accompanying sound record, it has been shown to be advantageous to provide the magenta component in the outermost layer of a monopack structure as described in copending application Serial Number 634,255 filed December 11, 1945, now U. S. Patent No. 2,551,086. Such an arrangement may be readily achieved with the present process, while maintaining the automatic masking.

In practice, moreover, the deviations from ideal maskingwhich may be actually obtainable, can be readily adjusted so as to place emphasis on superior reproduction of reds, blues, or greens in accordance with the requirements at hand. Controls of this type may be exercised in the present process since it is possible to use any combination of layer sensitivity and distribution of color generating elements, thus making the process possess great flexibility and versatility not found in previously proposed methods.

Suitable specific compounds are those derived from metanilic acid, sulfanilic acid, anthranilic acid, m-aminobenzoic acid, p-aminobenzoic acid, o-chloroaniline, p-chloroaniline, cyano-anilines or m-aminobenzotrifluoride, naphthionic acid, m-xylidine, 2-naphthylamine-6,8-disulfonic acid, and l-chloro-Z-aminotoluene. Although any other diazo compounds may be employed, those listed are well suited to producin colorless or nearly colorless reaction products from conventional yellow color formers while yielding the desired orange and yellow masks from the cyan and magenta components, respectively.

Among the useful stabilized diazo salts are the zinc chloride complexes and organic stabilized diazos. There can also be used derivatives of diazo compounds from which diazo compounds can be generated, e. g., diazoiminos, triazines and nitrosoamines and anti-diazotates.

Different diazo salts may be employed, for example, by treating the outermost layer of a monopack structure with a diazo salt solution of such composition as to retard the penetration of the diazonium compound, thereby limiting or restricting its action to an upper layer in the monopack structure. Subsequently, a diiferent diazonium compound may be caused to react upon the second, third, or lowermost layer either in separate stages or simultaneously. Such a procedure may be particularly advantageous in order to completely couple the coupling component in the outermost layer with a diazonium compound which yields thereby a substantially colorless or extremely pale yellow azo dye. This procedure may be employed when no integral mask is required to be introduced into the outermost layer, i. e., that carrying the yellow subtractive component. Following the complete coupling of this layer a different diazonium compound may be utilized to yield the desired mask for the remaining subtractive component.

A large number of other diazonium compounds is available for use in the alternative procedure just described. Among such stabilized salts which may be employed are the diazo salts from the following amines: meta-chloroaniline, meta-nitropara-anisidine, ortho-aminoazotoluene, l-aminoanthraquinone, 5-nitro-2-aminoanisole, metanitro-para-toluidine, 4-chloro-2-nitroaniline, 4- chloro-2-aminoanisole, 2,5-dichloroaniline, 4- nitro-Z-aminoanisole, 4-chloro-2-nitroaniline and the tetrazo salt from o-dianisidine. As stated above, the zinc chloride and other stabilized salts can be used.

Dye coupling reactions other than azo coupling similarly may be employed in order to produce one or more integral masks by reaction with residual or unused color formers. Other reducing agents which are capable of undergoing coupling in their oxidized form may be employed; 1. e., 1,4- naphthalene diamine-Y-sulfonic acid is a color coupling developer and yields a yellow color upon reaction with l-phenyl-3-methyl-pyrazolone-5 and thereby may be utilized to produce a mask for correction of the undesired blue absorption films is the preferred basis of rawstocks to be used in the masking processing since such stocks will withstand wide variations in processing, including temperature. The process itself is particularly advantageous for the production of intermediate color dupes in motion picture production whereby final release prints may be prepared in unlimited quantity without the necessity for registration printing and without attendant color degradation.

Multilayer films containing non-diffusing com pounds in conventional colloid silver halide emulsions may be utilized for masking procedures of similar type, although their use does not afford the latitude in processing that is possible with the hydrophilic color-former polymer structures. Many combinations of steps may be employed in processes of color reproduction for still and motion pictures in which the masking procedure may occur as an initial or as an intermediate step in the complete process. More than one masking step may be included in the complete process if several subtractive stages are involved.

In order to control the rate or extent of the supplementary dye generating reactions so as to yield the exact density and contrast which is required in the individual masks, it may be desirable to employ surface active agents which have the efiect of limiting or retarding the rate of consumption of dye-formingagent in the same manner that such agents are employed in textile dyeing to control rate of exhaustion of dye baths thereby producing level dyeing.

The invention will be further illustrated but is not intended to be limited by the following examples.

Example I A photographic element comprising a trans-- parent support and a light-sensitive silver halide layer utilizing as the colloid binding medium a hydrophilic polyvinyl acetal color former containing several naphthol sulfonamide groupings of the structure:

momnQ H obtained as described in United States Patent 2,423,572, was exposed and developed for ten minutes in a color developer of the composition:

p-Amino-N-diethylaniline hydrochloride V2.5 orange.

T again, the element was bathed for five minutes in a diazonium salt solution prepared as follows:

-To 20 cc. of 10% aqueous sodium hydroxide, 8.7 grams of sulfanilic acid were added. The mixture was stirred until solution was complete and then cooled to 5 C. and acidified with 13.5 cc. of concentrated hydrochloric acid. Stirring was maintained in order to secure fine particles of the amine hydrochloride. Cracked ice was added to the mixture so as to maintain a temperature of to C. and a solution of 3.5 grams of sodium nitrite in cc. of water was added with continued stirring. After standing one-half hour, water and cracked ice were added to make up the total volume to about 500 cc. Solid sodium acetate was added until disappearance of a positive test for hydrochloric acid with Congo red test paper. The pH of the solution was about 5.0. The entire solution was filtered and diluted to 1 liter.

To generate a colored mask the washed film strip was bathed for five minutes in a 12.5 cc. portion of the diaz-o solution which had been diluted to 100 cc. After shaking off the surface liquid, the strip was immersed in a solution of 1% ammonia for three minutes, washed thoroughly, and dried. The steps of a graduated exposure on the strip had substantially uniform density to blue and green light and good contrast to red light. The color of the dye mask Example II 1 A photographic element characterized by colorcoupling groupings of the structure:

OONH H 0 O as described in United States application Serial Number 9330 now U. S. Patent No. 2,513,190 filed February 18, 1948, produces a yellow color upon coupling development and a substantially colorless reaction product upon treatment with diazotized sulfanilic acid.

Example III Elements in which the light-sensitive layers were the same as those described in Example I were processed by color-coupling development, followed by a second color generating reaction employing a solution of diazotized-p-aminobenzoic acid. As in the first example, an orange 8. mask was obtained from the element yielding a cyan image from color-coupling development, a yellow mask from the magenta element, and a substantially colorless reaction product from the yellow element.

Example IV A photographic element of a type similar to that described in Example I, but characterized by color-former nuclei of the structure:

CH: --0 ONHQ H dlsclosed in application Serial No. 19,155 filed April 5, 1948 now U. S. Patent No. 2,489,655, was processed in two stages; first, by color development with a p-amino-N-diethylaniline developer solution as described in Example I, and then by coupling with diazotized sulfanilic acid. A minus-red dye image with a superimposed blue and green absorbing mask was obtained.

If the completely processed film element of this example is bathed before drying in a dilute solution of acetic acid or in a buffer solution of about pH 5.0, the color of the mask image is altered to a deeper shade of orange. This treatment has no eifect on the color-developed image or upon the mask image of the magenta and yellow elements of Example I.

Example V A photographic element of a m-(3-methylsalicylamido) -benzaldehyde polyvinyl acetal similar to that employed in Example IV was exposed and color-developed in the usual manner and several samples were then treated at room temperature with .5% solutions of stabilized diazo compounds as follows to give masks of the color shown in the table:

Color of Dye Diazo Salt of Amino Mask m-chloroaniline Orange. m-nitro-p-anisidine. Do. o-amino-azotoluene. Light Red. laminoanthmquinone. -1 Red.

E-nitro-Z-aminoanisola. Magenta.

m-nitro-p-toluidine Orange. 4-chloro-2-nitroaniline Dark Orange. -chloro-2-aminoanisole. range. 2,5-dichloroaniline Yellow 4-nitro-2-aminoanisole.. Orange o-dianisidine Bed.

Ewample VI Example VII A result similar to that of Example VI was obtained by bathing the color-developed sample, after fixing and washing, in the solution of the aniline-diazoamino derivative. Hydrolysis and sample in an atmosphere of about 100% relative humidity at a temperature of about 90 to 100 C.

Example VIII A multilayer film element having the following strata, in order, on a transparent support:

1. An emulsion layer for color-development of a cyan image like that of Example I and sensitized for red light.

' 2. A thin colorless separator layer of a hydrophilic hydrolyzed ethylene vinyl acetate interpolymer.

3. An emulsion layer for color-development or" a yellow image like that of Example I and sensitized for green light.

4. A separator like layer 2.

5. An emulsion layer for color development of magenta like that of Example I and containing a yellow filter dye, e. g., Tartrazine (Colour Index No. 640) was exposed to a graduated step tablet and through three red, green and blue primary filters.

The element was processed as in Example I by color developing with p-amino-diethylaniline, bleaching, fixing, washing, and treating with diazotized sulfanilic acid of the same strength. A multicolor negative image with superimposed orange and yellow masks was obtained.

A similar element was color-developed, washed, U

bleached, fixed, washed and dried to yield a multicolor image without masks. The two processed samples were then printed directly onto a multilayer element of the same construction. The color temperature of the printing source and the duration of the printing exposure were adjusted in each case so as to produce equal, neutral densities, from corresponding highlight areas, in the two reproductions. Marked improvement in the reproduction of the red, green and blue primary colors is apparent in the case of the print from the masked negative as compared to the unmasked print.

Example IX A photographic element characterized by pyrazolone nuclei of the type used in Example I was exposed and processed by color coupling development to yield a magenta dye image. Without fixing, the element was washed thoroughly, re-exposed and redeveloped in a developer like that employed in Example I, but containing in place of the p-amino-diethylaniline, 2 grams of 1,4-naphthylenediamine-'I-sulfonic acid. After washing, the element was bleached, fixed and rewashed whereby a primary magenta image and a superposed yellow mask image were produced.

If in the procedure of this example, the second development step is carried out with an aromatic hydrazine or hydrazine derivative, superposed masks may be generated under conditions of control which may be regulated by variation in second exposure, duration of treatment, and other conditions. For example, the second colorgenerating step of this example, which is used for formation of the masking image by exposure and development, can be modified by using a developer solution of a hydrazine as described in United States Patent 2,220,929 (Example I). Alternatively, hydrazine derivatives such as N- acyl-N-arylhydrazines (French Patent 925,609) or sulfonhydrazides (disclosed in United States Patent 2,424,256) may be employed for developing the secondary masking images by reduction of exposed silver salts and coupling with residual color-former nuclei.

:10 Example X Photographic elements of the three types described in Examples I, II, and III above were bathed in a fixer to dissolve silver halides, then washed and dried. Samples of each of the elements so prepared were then bathed in solutions of diazonium salts of the amines listed in the table below. These solutions were prepared by diazotization of the several amines, adjustment (with sodium acetate) of the pH of the resulting diazonium salt solutions to neutrality, and dilution of the solutions with water to yield concentrations of 0.05% based on the weights of the amines used.

Column 1 of the table lists the amines from 'which the diazonium salt solutions were prepared.

Heading columns 2, 3, and 4 are the colors which the three respective photographic elements yielded when exposed and developed as in Examples I, II, and III above. Also in these columns are listed the dye colors which the respective elements yielded when treated in diazonium salt solutions as in the preceding paragraph.

Amine cal) Comparison of the dye colors listed in the above table with those described in Examples I, II, and III reveals that these colors are proper for use as integral masks to cancel all or part of the undesirable light absorptions of subtractive color dyes as described earlier.

Exampl XI Samples of a photographic element of the type described in Examples IV and V were prepared and treated in diazonium salt solutions as in Example X above. A yellow dye color resulted from such treatment in solutions of the diazonium salts of o-chloro-aniline, p-chloro-aniline, 2-naphthylamine-6,8-disulfonic acid, m-amino-benzotrifluoride, naphthionic acid, and metanilic acid.

Example XII A photographic element like that of Example I was prepared by substituting for the hydrophilic color former 4-methoxy-3-(benzoylacetamido) benzaldehyde polyvinyl acetal. The latter compound can be made after the manner taught in United States Patent 2,310,943 by acetalizing polyvinyl alcohol with i-methoxy-B-(benzoylacetamido benzaldehyde or its ethylene glycol acetal.

The element was then exposed and developed in a developer similar to that in Example I. The developed color resulting from coupling (with the p-amino-diethylaniline hydrochloride of the developer) was yellow. After washing, bleaching, fixing, and washing again, the element was bathed for five minutes in a diazonium salt solution prepared by diazotizing sulfanilic acid, adjusting to neutral pH with sodium acetate, and diluting to 0.05% concentration (based on the weight of sulfanilic acid). No coloration of the 11 element was produced by the treatment in the diazonium salt solution. Thus this element exhibits properties ideal for theyellow polymer layer of a film described earlier as a negative employing integral masking.

Similar effects may be observed when the original primary color exposures are made from an original colored scene or from color separation positives of the original scene by means of red, green and blue primary color filter exposures.

The invention has the additional advantage that it provides a practical and effective process for correcting the undesirable absorption of quinoneimine and azomethine dye images in the reproduction of subtractive originals. A further advantage is that the process provides a full neutral scale, and saturated orange, red and yellow colors are produced. .A still further advantage is that good control of color densities is achieved and their relative proportions in the grays are the same as if no masking had been employed,

but are altered in areas corresponding to strong blues, greens, reds, and yellows.

As many widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as defined by the claims.

What is claimed is:

1. The process of making integral color masking images in a multicolor picture made up of subtractive color images which comprises developing with a primary aromatic amino color developing agent, an exposed multilayer photographic film bearing a colloid silver halide emulsion layer initially sensitized to light from one primary color region of the spectrum and including as a cyan color former a m-(3-methylsalicylamido)benzaldehyde polyvinyl acetal, a colloid silver halide emulsion layer initially sensitized to light of a second primary color region of the spectrum including as a magenta color former a m- [p- (3-methy1'1-pyrazolyl) benzamido] -benzaldehyde polyvinyl acetal and a colloid silver halide emulsion layer initially sensitized to a third primary color region of the visible spectrum including as a yellow color former a m-ben zoylacetamidobenzaldehyde polyvinyl acetal, said film initially bearing a stratum containing a yellow filter dye and being arranged so that blue light will not expose two of such emulsion layers, treating the developed element in at least one aqueous solution containing a diazonium salt and removing the silver and silver salts from the resulting film.

2. A process as set forth in claim 1 wherein said polyvinyl acetals are the sole binding agents for the silver halides in the respective layers.

3. A process as set forth in claim 2 wherein a single diazonium salt solution is used.

4. A process as set forth in claim 8 wherein said salt is diazotized sulfanilic acid.

ANDREW BRADSHAW JENNINGS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,193,931 Michaelis Mar. 19, 1940 2,297,732 Woodward Oct. 6, 1942 2,306,410 Schinzel Dec. 29, 1942 2,449,966 Hanson Sept. 21, 1948 2,431,996 Duerr et al Dec. 2, 1947 2,518,739 Young Aug. 15, 1950 

1. THE PROCESS OF MAKING INTEGRAL COLOR MASKING IMAGES IN A MULTICOLOR PICTURE MADE UP OF SUBTRACTIVE COLOR IMAGES WHICH COMPRISES DEVELOPING WITH A PRIMARY AROMATIC AMINO COLOR DEVELOPING AGENT, AN EXPOSED MULTILAYER PHOTOGRAPHIC FILM BEARING A COLLOIC SILVER HALIDE EMULSION LAYER INITIALLY SENSITIZED TO LIGHT FROM ONE PRIMARY COLOR REGION OF THE SPECTRUM AND INCLUDING AS A CYAN COLOR FORMER A M-(3-METHYLSALICYLAMIDO) BENZALDEHYDE POLYVINYL ACETAL, A COLLOID SILVER HALIDE EMULSION LAYER INITIALLY SENSITIZED TO LIGHT OF A SECOND PRIMARY COLOR REGION OF THE SPECTRUM INCLUDING AS A MAGENTA COLOR FORMER A M-(P-(3-METHYL-L-PYRAZOLY) BENZAMIDO)-BENZALDEHYDE POLYVINYL ACETAL AND A COLLOID SILVER HALIDE EMULSION LAYER INITIALLY SENSITIZED TO A THIRD PRIMARY COLOR REGION OF THE VISIBLE SPECTRUM INCLUDING AS A YELLOW COLOR FORMER A M-BENZOYLACETAMIDOBENZALDEHYDE POLYVINYL ACETAL, SAID FILM INITIALLY BEARING A STRATUM CONTAINING A YELLOW FILTER DYE AND BEING ARRANGED SO THAT BLUE LIGHT WILL NOT EXPOSE TWO OF SUCH EMULSION LAYERS, TREATING THE DEVELOPED ELEMENT IN AT LEAST ONE AQUEOUS SOLUTION CONTAINING A DIAZONIUM SALT AND REMOVING THE SILVER AND SILVER SALTS FROM THE RESULTING FILM.
 2. A PROCESS AS SET FORTH IN CLAIM 1 WHEREIN SAID POLYVINYL ACETALS ARE THE SOLE BINDING AGENTS FOR THE SILVER HALIDES IN THE RESPECTIVE LAYERS. 